Make a matrix with input inside a DIV by mixing input values

Make a matrix with input inside a DIV by mixing input values

Take a look at this:
<div id="main">
<div id="a">
<input value="1" />
<input value="2" />
<input value="3" />
</div>
<div id="b">
<input value="4" />
<input value="5" />
</div>
</div>
I need to get each input value inside div#a and each input value in div#b
and build a matrix/mixing of those values, taking the same example as
before, this is what the code should return:
<div id="mixed">
<input value="1" /><input value="4" />
<input value="1" /><input value="5" />
<input value="2" /><input value="4" />
<input value="2" /><input value="5" />
<input value="3" /><input value="4" />
<input value="3" /><input value="5" />
</div>
I have tried to move inside div#main using this code:
$("#main div").each(function() {
var that = $(this);
console.log("that.attr('id')");
});
But console.log() never logs something so I must doing something wrong.
This is a advanced topic for me and need some help, any?
UPDATE
At this point I have this maded:
$("#choices div").each(function() {
var that = $(this);
that.each(function() {
var thati = $(this);
console.log(thati);
});
});
And I think in the second .each() is where I can get the input values and
try to build the matrix